In the current state of the art, there are different documents that are described and analyzed below.
The invention patent (WO 2014037093 A1) discloses a system for a global three-dimensional correction of the curvatures of the spine, in which the fixation devices or pedicle screws are not polyaxial, since it uses uniaxial screws in different directions to correct the spine; however, it uses different screws on both sides and it does not mention a screw that can acts as a polyaxial, uniaxial or fixed screw.
The document ES 2455122 T3 describes a bone anchoring device comprising a receiving part to house a rod that engages a bone anchoring element that has a shank and a head, the bone anchoring element being a polyaxial screw wherein the head is clamped from the side to fix the rotational position of the bone screw and wherein a locking element is provided to secure the rod in the receiving part.
The aim is to provide an improved receiving part consisting of few parts and that is better handled during the surgical operation. Specifically, the receive the rod (6) and a housing space (19) for accommodating a head (3) of the bone anchoring element (1), the housing space (19) that has an opening (18) for introducing the head, and a pressure element (8) located at least in part in the housing space (19), the pressure element have a flexible part (82) for holding the head; wherein the pressure element (8) can adopt in the body of the receiving part (5) an insertion position wherein it is possible to introduce the head, a locking position wherein the head is locked in the receiving part and a pre-locking position wherein the head is fixed by the pre-tension exerted by the pressure element, and in which the pressure element (8) is maintained in the pre-locking position by means of an elastic force, the elastic force being generated by a spring part (9a, 9b, 92) in the pressure element or in the body of the receiving part that works with a stop (93) in the body of the receiving part (5) or the pressure element, respectively, the stop acting as a stop to ensure the pre-locking position; said intention describes a polyaxial screw that can be locked at a predetermined point, unlike the present invention, which once locked does not allow movement in any direction. The present invention is characterized either by converting the screw into a conventional fixed screw or, in the position that is locked, allowing the movement on only a coronal or sagittal axis. The aim of the present invention is not to achieve a screw that can be locked in a fixed position, but rather obtain, with a single screw, all the options that exist in the market of screws that are moveable in different directions and that are fixed, greatly simplifying the task and obtaining a screw with greater versatility; furthermore, after implementation, it allows a polyaxial screw to convert into a fixed or uniaxial screw.
The document ES 2525046 T3, of the same applicant as the previous document, describes a bone anchoring system including an anchoring element (1) with a shank (2) for anchoring it to the bone and a head (3), a housing part (5) that has an upper end (5a) and a lower end (5b), a channel (11) to house a rod (6) near the upper end and a housing space (9a, 9b) to house the head near the lower end, the housing space having an opening (10) towards the lower end that is sized to allow the introduction of the head (3) from the lower end; a pressure element (8) that is located at least partly in the housing space and that has a flexible part (85) for immobilizing the head; the anchoring element being able to rotate with respect to the housing part and being fixed at an angle by moving the pressure element inside the housing space such that the head (3) is locked inside the flexible part (85) of the pressure element, wherein the pressure element includes a protrusion (83, 83′, 83″) that engages an inlet section (9b, 13), that has an enlarged diameter in the housing part, when the pressure element is inserted into the housing part to prevent the loss of the pressure element from the housing part, and an inlet (11c) being provided in the bottom of the inlet (11c) channel (11) that is configured to engage the protrusion (83, 83′, 83″), such that when the pressure element is inserted into the housing part with the protrusion (83, 83′, 83″) pointing to the inside of the channel (11), the protrusion (83, 83′, 83″) reaches the inlet section (9b, 13) through the inlet (11c), and in this situation, the pressure element can rotate inside the housing part.
Said document describes a system similar to the previous systems, which works as a polyaxial system and wherein the screw head is locked by means of an insert, the insert surrounds the head and upon closing, it closes on the head, clamping it. The system permits the entry of the screw head from inside the cap, as well as from the lower end of the cap. Like the other aforementioned cases, this screw always acts as a polyaxial screw until it is locked. The ring of the present invention along with the tabs secured to it act on the screw before the system is closed (introduction of the reducing bar and closure with the top) and its function is to lock movement in a specific direction, or in all directions (or it does not lock). Once the reducing bar is introduced and it is fixed with the closing lid, the system is locked by the pressure of the coupling element on the screw head, being fixed at that point.
The document WO 2009055400 A1 discloses a polyaxial screw assembly for insertion into the spinal region of the patient, which includes a pedicle screw (110), a coupling element (130), a threaded part (50) and a case or cap (70). The pedicle screw includes a shank that has a helical thread and a head at one end. The coupling element is placed on the upper part of the pedicle screw and releasably engages portions of the screw head. The coupling element and the pedicle screw are positioned inside a distal portion of the cap. The pedicle screw is slid through an opening in the threaded part and is thread into the distal portion of the cap to retain the coupling element and the pedicle screw inside the cap. The pedicle screw is rotatable and pivotable with respect to the cap. Compressing the coupling element inside the cap locks the pedicle screw, which is easily secured in a desired orientation.
Said invention uses a polyaxial screw system capable of being locked in a specific position, unlike the present invention, which does not explicitly seek to lock the screw in a specific position, but rather aims to have the screw work in different directions according to the necessary demands.
The document WO 2007141347 A1 discloses a vertebral fixation device fundamentally consisting of a pedicle screw (1) with a partially spherical head (2), a rosette (3, 3′, 3″) provided with an upper promontory (4) from which flexible slats (5) come down to press on and fix the position of the head with a specific orientation, a tulip (6) with lateral notches (7) opposite each other and a lower cavity (18) that holds the rosette, a bar (8) that constitutes the link with the other devices fixed to other vertebrae, which is housed in the lateral notches (7) and which rests against the upper head of the rosette (3, 3′, 3″), a closing lid (9) with circular openings (10) through which the bar passes, which moves in an axial direction on the outer face of the tulip, and a closing screw (11) which is threaded on the inside the tulip (6) and drags the closing lid (9) along with it in its movement and fixes the bar (8) against one or more of the upper promontories of the rosette; similar to all the preceding systems, said system describes a screw that is not completely polyaxial and which seeks to successfully fix the screw at a specific point.
The document MX 2011000917 A discloses locking mechanisms (100) and methods of fixation, such as the fixation of a fixation device (104) like a bone screw and a rod (106) to the spine. The locking mechanism comprises a body (102) having a lower portion and a side portion, in which the side portion is configured to receive a rod (106); a fixation device (104) extending at least partially through a hole in the lower portion of the body; and a rod seat (110) between the rod and the fixation device, the rod seat having an upper portion configured to interact with the rod and a lower portion configured to receive part of the fixation device (104), specifically the spherical head (140) thereof, and an adjusting screw (112), in which the rod seat (110) is configured to be separated into two parts (110a-110b) when the rod (106) exerts force on the upper portion of the rod seat (110) and the fixation device (104) limits the movement of the rod seat towards the lower position of the body (102).
Said document reflects a polyaxial screw system that is locked in a fixed position by the pressure of the different coupling parts such that once the (closed) system is locked, the screw remains fixed in a position. The system is similar to that of the present invention in that it locks the screw by means of a coupling element; however, the fundamental difference is in what happens before locking. The function of the tabs in our screw is to lock the movement in specific directions (or in none) such that the screw supports certain stresses but not others (by having freedom of movement on some planes), and here the difference lies in the movement of the screw during the implementation of the reducing bar that connects the different vertebrae, since once the system has been closed and the reducing bar is properly placed, the system is locked with the screw fixed in that direction.
The document WO 2009014540 A1, which shares one of its inventors with the previous document and is similar thereto, discloses a locking mechanism (100) such as that of the previous patent, which adds an insert (108), such that the locking mechanism (100) has a fixation device (104) extending through a hole (118) of a main body (102), which has a side portion (120) that receives a rod (106). The partially spherical insert (108) surrounds the head (140) of the fixation device. A rod seat (110) has an opening for engaging an upper surface of the insert, and it applies forces to the insert that have both lateral and vertical components which will be applied to the head of the fixation device.
In this case, the rod seat (110) and insert (108) parts, which are engageable, have some similarity to the coupling element (3) and the adjusting ring (4), except for the pressure that causes the closure of the insert on the head thereof, since it locks the head and prevents the movement thereof. As in the other systems described, the mechanism seeks to lock the screw in a position to prevent the movement of the screw-reducing bar assembly. This is also achieved in the present invention when the reducing bar has closed inside the screw, even though the insert does not impede the movement, but rather limit movement in a certain direction when needed or allow it to move in all directions if necessary. The locking of the screw is only the final part, but that characterized in the present invention is the limitation of the movement of the screw in certain directions.
In the document ES 2302115 T3, an embodiment is shown in which an implant for locking a screw at any angle comprises a screw head retaining insert (84′) that comprises a partially spherical seat (96). The outer wall of the insert element (84′) is in the form of outwardly tapering tabs (98) that have an inwardly tapered inner wall (100). The insert element has a recess (102) which allows for the hinging or collapsing of the insert element about its diameter. The rod retaining ring (12′″) comprises a cylindrical opening (104) and a seat for said insert, including axially extending slots (106) for receiving the outwardly tapering tabs (98). Thus, alignment means for aligning the insert element with respect to its seating position within the ring (121 is provided. This alignment can also be used for aligning any of the inserts in any of the embodiments by providing outer tabs engaging in predefined slots. Said document describes technical characteristics similar to those described in the previous documents, and with respect to the same, there are the same differences commented in the previous documents.